In recent years, electronic cameras are widely used. This kind of the electronic camera is provided with an image sensor for converting an optical subject image into an electrical signal. With respect to the image sensor, a CCD type and a CMOS type are mainly used. As a trend, the CCD image sensor is widely utilized because of advantage concerning high pixel density.
As to the CCD image sensor, there are an interline-type CCD, a frame-transfer-type CCD and so forth. For instance, the interline-type CCD is composed of a large number of pixels, a vertical transfer pass (vertical CCD), a horizontal transfer path (horizontal CCD), a charge detecting amplifier and so forth. The pixels comprise photo diodes and are arranged in a matrix. The vertical transfer path is provided for each pixel row including the pixels arranged in a vertical direction. Signal charges photoelectrically converted in the respective pixels are transferred to the vertical transfer path through a transfer gate and are sequentially forwarded thereby in a vertical direction. The horizontal transfer path is disposed at an end of the vertical transfer paths to receive the signal charges forwarded from the respective vertical transfer paths. The received signal charges are horizontally forwarded by the horizontal transfer path. The charge detecting amplifier converts the signal charge, which has been forwarded from the horizontal transfer path, into a voltage to be outputted.
Instead of the horizontal transfer path, the charge detecting amplifier may be disposed at an end of each of the vertical transfer paths. In this case, output of the respective charge detecting amplifiers is read by a horizontal scanning circuit. An image sensor having such structure is described in Japanese Patent Laid-Open Publication No. 2002-135656.
Some of the electronic cameras have a moving-image mode for recording a moving image, besides a still-image mode for taking a still image. Further, some of the electronic cameras have a through-image outputting function for displaying a subject on a liquid-crystal display or the like equipped on the electronic camera. When the moving-image mode is executed or when the through image is displayed, the image sensor is activated at a rate of 30 frames per second (30 fps), for example, in order to smoothly display the motion of the reproduced subject image. In recent years, however, the image sensor is improved so as to have high pixel density and it is difficult in some cases to transfer the charge of all the pixels and to output the signal during a one-frame period. In such cases, the CCD image sensor performs vertical pixel skipping and pixel mixture to vertically thin the pixels (line) on the image sensor. Incidentally, the pixel skipping and the pixel mixture are easily performed in the vertical direction by controlling the transfer gate.
Meanwhile, it is known that a defect occurs on the image sensor due to partial crystal faulty of a semiconductor and so forth. The defect of the image sensor deteriorates image quality. As to this kind of the defect, there is the defect of a dot shape (hereinafter referred to as dot defect) caused by the defective pixel. Beside the dot defect, there is the other defect which is caused by the vertical transfer path and has a line shape extending in the vertical direction (hereinafter, this sort of the defect is referred to as line defect). The line defect of a white line shape is caused by applying charge, which has no relation to the signal charge, to the vertical transfer path. Besides this, there is line-shaped density unevenness caused by a low transfer rate of a part of the vertical transfer path. However, it is difficult to produce the image sensor having no pixel and no vertical transfer path by which the defect is caused. Further, after producing the image sensor, the defect is likely to occur when ultraenergetic particles of cosmic rays and so forth enter the image sensor.
By the way, although the occurrence of the dot defect to be caused by the defective pixel may be avoided to some extent, it has been impossible to avoid the occurrence of the line defect because the line defect is caused by the vertical transfer path. Meanwhile, correction technique is established for not only the dot defect but also the line defect by performing defect correction for the output signal sent from the image sensor. However, when the many line defects occur, a processing period required for correcting the defects is long and a memory is excessively used for the purpose of correcting the defects. Thus, there is a problem in that a frame rate, a shooting number and so forth are often restricted. In addition, there is another problem in that image quality is likely to be deteriorated, although the line defects are corrected.